Combination crude distillation and olefin production process



Aug. 23, 1960 w. s. CRAFT ETAL 2,950,241

COMBINATION CRUDE DISTILLATION AND OLEFIN PRODUCTION PROCESS Filed DEC.9, 1957 22 TO LIGHT ENDS PLANT I 24 25 I as 21 J\- I I IlATOR STRIPPERIII: g o'' JAuT 1:111:51 GA$ OIL N TTTTTY III/35 A REDUCED CRUDE FROMSTILL I ;-Z I CAT. CRACKING PRODUCTS RESIDUUM GASEOUS PARAFFIN CRACK|NGSTAGE ifim FROM GASEOUS OLEFIN RECOVERY PLANT WILLIAM S. CRAFT WILLIAMM. SMITH CARTER E. PORTER INVENTORS ilddj ll Patented Aug. 23, 196.0

COMBINATION CRUDE DISTILLATION AND OLEFIN PRODUCTION PROCESS William 5.Craft, William M. Smith, and Carter E. Porter,

Cranford, N.J., assignors to Esso Research and Engineering Company, acorporation of Delaware Filed Dec. 9, 1957, Ser. No. 701,480

4 Claims. (Cl. 208-78) The present invention relates to an improvedmethod for the conversion of crude petroleum into more valuablehydrocarbon oil products. More specifically, it is concerned withobtaining maximum yields of low boiling products of the motor fuel andgas oil ranges and minimum yields of heavy products such as fuel oilsand tars, while at the same time producing high quality ethylene orpropylene with a minimum of processing steps and a substantially reducedinvestment and operating cost.

In its broadest aspect, the present invention involves a series ofintegrated distillation, catalytic and thermal conversion stages whereinproducts from these stages are conducted to a single productfractionation step and treated therein in a manner such that reducedcrude obtained as liquid residue of a crude distillation is stripped ofrelatively low boiling constituents. More particularly, the inventionpertains to a combination process of the type wherein one of theconversion stages is high temperature cracking of ethane or propane.

In conventional combination crude oil distillation and conversionprocesses, the recovery of maximum yields of motor fuel and heating oilproducts has been usually accomplished by subjecting light and heavynaphtha fractions from a crude still to further fractionation and, ifdesired, to suitable thermal or catalytic refining treatments such asreformation, isomerization, hydroforrning, alkylation, etc. A gas oilfraction from the crude still is subjected to thermal or catalyticcracking to obtain lower boiling products which are subsequentlyfractionated. The reduced crude is generally subjected to a furtherdistillation at reduced pressures to produce tar and additional lowboiling products, principally gas oil to be processed with the gas oilfraction from the crude still as mentioned above. These processesnormally require as many product fractionators as there are strippingand conversion stages, yielding a plurality of streams of products ofdesirable boiling range. For economical heat recovery, much heatexchange apparatus is required both within each unit and in combinationbetween units. Vast tank facilities must be provided to permit storageof the various products prior to blending in desired proportions. Thevacuum distillation equipment normally used for working up the reducedcrude is expensive with respect to investment, operation andmaintenance. As a result of these complications, conventional typecombination processes must be operated on a relatively large scale to beeconomical. Normally, refining capacities in excess of, say, about20,000 bbls. per day of crude are required to make operations of thistype pay, while smaller refineries must be designed on the basis of anoften undesirably high output of heavy fuel oil and other products of arelatively low commercial value.

The present invention utilizes effluent from an ethane or propanecracker, together with efliuent from a catalytic cracker or otherconversion unit, in a combination fractionator for furnishing thepartial pressure effect and heat to help strip heavy gas oil from thereduced crude without need of vacuum equipment.

The present invention also provides an improved method for theintegrated production of ethylene or propylene in a combination unittype refinery. These olefins are currently manufactured principally byone of two methods. They can be recovered from existing refinery gasstreams, for example, from the gas from a fluid catalytic cracker orsteam cracking unit. They can be obtained by cracking ethane or propane.

The method of recovering C to C olefins from the.

cracked gases is similar in both of these cases. Where ethylene isrecovered from the eflluent of steam cracking or from ethane or propanecracking, the very hot reactor effluent has to be quenched quickly. Thequenching requires circulation of large amounts of quenching liquid,e.g. water and oil.

In normal operation of the combination unit, reduced crude has beenpassed generally to an intermediate part of a fractionating column. Insome of these units, naphtha conversion effluent has been fed to thefractionating column at a point below the feed point of the reducedcrude, substantially at the temperature of the conversion stage. In someinstances a light virgin naphtha has been supplied to the fractionatingcolumn likewise at a point below the reduced crude feed point aftersuitable additional heating, if desired. Various final product streamshave been recovered from the fractionator which would include a fuel gasoverhead, a low boiling fraction of motor fuel boiling range, a heatingoil fraction, a gas oil fraction, and a heavy bottoms fraction of thefuel oil range. The gas oil fraction is sent to a catalytic crackingstage to be converted into additional amounts of motor fuel, diesel oil,gas oil range cycle stock, and heavy bottoms. It has been considereddesirable to pass the catalytically cracked gas oil products to a pointbelow the reduced crude feed. In this manner, the reduced crude orequivalent thereof was intended to be subjected to countercurrentheating, vaporization and stripping actions with vapors from the gas oilcracking process as well as with the virgin and reformed naphtha vapors.

When operating substantially as described above, extremely large volumesof process vapors are required and heat has to be supplied for thereduced crude stripping in order to keep the volume of heavyresiduurn'finally produced at a minimum. Also for ethylene recovery thelight gases from ethane cracking and catalytic cracking are combinedbefore the recovery operation.

The present invention affords certain advantages that.

will be apparent from the description following.

In the present invention, ethane or propane cracking is integrated intoa combination reduced crude and catalytic cracked gas oil productfractionator. A partially quenched efiluent from such an ethane orpropane cracking operation is introduced into the bottom of acombination product fractionator for reduced crude stripping andcatalytic cracked product fractionation. More specifically, thepartially quenched eflluent from the ethaneor propane cracking serves tohelp vaporize gas oil from the reduced crude and is itself at the sametime further quenched and cooled by contact with the residual portionsof the reduced crude. The ethylene or propylene produced in the ethaneor propane cracking step is passed through the fractionation zone, maybe separated from condensible vapors of higher boiling hydrocarbons andmay be then sent to a light ends separation plant wherein absorber drygas is separated from other hydrocarbons. The absorber dry gas, e.g.ethylene or propylene, may be subjected to an operation wherein theolefins produced in the ethane or propane cracking step are recoveredalong with a similar olefin product formed in the catalytic crackingstep. It is also a function of the olefin recovery process to separateout any methane invention will be best'understood from the more detaileddescription hereinafter which refers to the accompanying drawing,wherein a schematic flow diagram of the steps and means used in thepresent invention is shown.

Referring to the drawing, the reduced crude is passed from aconventionalatmospheric still outlet 17 to the lower portion of acombined product fractionator-stripper 15. The reduced crude enters thecombination unit substantially at the conditions of the still, that isat a temperature of about 650 to 7 F. and a pressure of about 5 to 15p.s.i.g. The efiluent from an ethane orpropane gas cracker 10, saideflluent leaving the cracking stage at about 1450 to -1550 F. and about5 to 15 p.s.i.g., is passed through line 11 wherein at least a portionof the eflluent is contacted with a quenching liquid introducedby meansof line 12 in order to lower the temperture of the cracking eflluent toabout 900 .to 1000 F. The stream is then passed by means of lines 11, 13or 14, or both 13 and 14, to the combination fractionator 15. Line 13leads directly from line 11 to the combination unit 15 at a point belowthe feed point of the reduced crude 17. Line 14 passes an efiluentstream of reaction products from a catalytic cracking process, thevapors of which are substantially at the catalytic crackingconditions900 to 1000 F. and about 5m 15 p.s.i.g. and which enter fractionator 15below the feed point of the reduced crude. The relative proportion ofthe efiluent 'from that is passed through line 13 directly to thecombination unit depends primarily on the amount of stream 11 that hasbeen contacted with the quench 4 may be made to US. 2,644,785 and US.2,777,801 for operation of the unit and other details of the process. Inthe present invention, the partial pressure efiect of the stream fromthe ethane or propane cracker 10 and the heat content thereof aresuificient to cause the gas oil constituents of the reduced crude tovaporize. A side stream of gas oil range hydrocarbons boiling in therange of 600 to 700 F. which is suitable as a catalytic cracking stockis withdrawn from an intermediate sec- 'tion of fractionator 15 via line1-8. This side stream product may serve as a quench liquid sent to line12. A heavy material containing non-distillable constituents of thecrude charged collects in the bottom zone of section a A of thecombination unit 15 from which it is withdrawn via line 16. t

It will be understood that although in the operation of a conventionalcombination fractionator other streams may be introduced or Withdrawn,such as a heating oil,

a a low boiling fraction of the motor fuel boiling range,

a line 25.

steam, etc.; for the purposes of the presnet invention,

the simplified drawing does not show all of these.

The gas and naphtha vapors leave the top of fractionator 15 through line21 at about 50 to 100 F. and 10 to 15 p.s.i.g. After passing throughcondenser 22,. the fractionator efiluent stream passes to a liquid andgas separator 23. From separator 23, the gaseous stream containing theolefins is withdrawn by line 24 and the liquid containing naphthahydrocarbon is withdrawn by V the light ends plant by line 27.

liquid from line 12. If'desired, all the effluent from.

liquid 12 and the addition of the cracker eflluent 11 to.

line 14 rather than having the cracked gases from line 11 pass directlyto thecombination unit 15 is to lower the.

temperature of the cracked gases from about 1450 to about 1550 F. as itleaves the gas cracking stage to about 900 to 1000 F. as it enters thefractionator 15. An indirect heat exchange means may be provided forthis purpose also, if desired.

The cracked gases and vapors supplied through lines 13 and 14 passupwardly through fractionator 15 against the downwardly flowing reducedcrude to strip the latter of vaporizable constituents. Fractionator 15comprises a lower stripping section A and an upper combinedfractionation section B. Both sections are provided with suitable knownmeans for improving the countercurrent .contact between downflowingliquid and upwardly flow- The gas stream in line 24 is also passed to alight ends separation plant in which the absorber dry gas containing Cand C and lighter hydrocarbons are separated from C and higherhydrocarbons. The absorber 'dry gas containing C or C and lighterhydrocarbons is next passed to a recovery system similar to aconventional ethylene recovery plant in which the ethylene or othergaseous olefins produced in the ethane or propane cracker 10 arerecovered along with any olefins'produced in the catalytic crackingstep, the outlet of which is 14. Methane and lighter gases are separatedout in this recovery plant 'and any ethane and/or propane present isrecovered,

separated, and recycled via line 9 to provide feed for the ethane orpropane cracking operation. 7

Representative operating data in demonstrating a preferred embodimentare given in the following example:

EXAMPLE 1 The combination fractionator was operated under the followingtabulated conditions:

Comliination fractionator Stripping zone conditions, 800 F. and 8p.s.i.g.

It is to be noted from the above that 10,745 barrels,

per day of gas oil constituents were recovered. If this process wereoperated without utilizing the product vapors from the ethane crackingunit, only approximately 5,000 to 6,000 barrels per day of gas oilconstituent would be recovered.

In the plant to which the above data pertain, a reduced crude enters thecombination unit at a temperature of about 650 to 700 F., preferablyabout 680 to 690- At least a portion of the liquid is refluxed by line26'to the combination unit 15 at a point near the F., a feed from acatalytic cracking stage enters the fractionation zone at a point belowthe feed point of the reduced crude at a temperature of about 900 to1000 F., preferably about 940 to 950 R, an efliuent from a C to Cparaffin high temperature cracking step which leaves the ethane orpropane cracking stage at about 1450 to 1550 F, and preferably about1530 to 1540 F. when cracking ethane after being partially quenched bycontacting said eflluent with either a gas oil product stream from thecombination unit or with a catalytic cracking feed, enters thefractionation zone at a point below the reduced crude feed point at atemperature of about 900 to 1000 R, preferably about 940 to 950 F., astream of gas oil stripped from the reduced crude is withdrawn from thefractionation zone at about 600 to 700 F, and preferably about 640 to650 F., a stream of heavy residuum leaves the bottom of the combinationunit at a temperature of about 580 to 650 F., preferably about 600 F.,and the absorber overhead product vapors leave the combination unit at atemperature of about 75 to 120 F., and preferably about 80 to 90 F.Suitable conditions for the stripping zone are temperatures in the rangeof 750 to 850 F. and preferably 790 to 820 F., and pressures in therange of 5 to 15 p.s.i.g., and preferably 8 to 12 p.s.i.g.

The process of the present invention secures efiicient heat recovery andthe elimination of the need for separate quenching equipment.

What is claimed is:

1. In a combination distillation and catalytic hydrocarbon conversionprocess the improvement which comprises passing a reduced crude oilcontaining a substantial quantity of hydrocarbon components boiling inthe gas oil boiling range into an intermediate part of a productfractionation zone operated at elevated temperatures and greater thanatmospheric pressure, passing a major portion of the efiluent vaporsfrom a C to C parafiin cracking zone operated at temperatures of 1450 to1550 F. directly to join a much greater volume of vapors supplied from acatalytic cracking zone operated at temperatures of 900 to 1000 F. thusrapidly quenching the high temperature efiluent from the paraflincracking process to a temperature in the range of 900 to 1000 F.,supplying the combined stream of hydrocarbon vapors from said quenchingoperationinto a lower part of the product fractionation zone, strippinggas oil components from said reduced crude, segregating and removing agas oil fraction from said fractionation zone and removing overheadproducts from said fractionation zone containing olefins produced insaid C to C cracking operation and naphtha from said catalytic crackingprocess. I

2. The process of claim 1 in which said stripping of gas oil componentsfrom the reduced crude is conducted at temperatures of about 750 to 850F. and pressures of about 5 to 15 p.s.i.g. and in which said gas oilproduct removed from the fractionation zone boils in the range of 600 to700 F.

3. A process according to claim 1 wherein a feed stream for said C to Cparaffin cracking operation is composed principally of ethane.

4. A process according to claim 1 wherein a feed stream for said C to Cparafiin cracking operation is composed principally of propane.

References Cited in the file of this patent UNITED STATES PATENTS2,777,801 Bittner et al- Ian. 15, 1957

1. IN A COMBINATION DISTILLATION AND CATALYTIC HYDROCARBON CONVERSIONPROCESS THE IMPROVEMENT WHICH COMPRISES PASSING A REDUCED CRUDE OILCONTAINING A SUBSTANTIAL QUANTITY OF HYDROCARBON COMPONENTS BOILING INTHE GAS OIL BOILING RANGE INTO AN INTERMEDIATE PART OF A PRODUCTFRACTIONATION ZONE OPERATED AT ELEVATED TEMPERATURES AND GREATER THANATMOSPHERIC PRESURE, PASSING A MAJOR PORTION OF THE EFFLUENT VAPORS FROMA C2 TO C3 PARAFFIN CRACKING ZONE OPERATED AT TEMPERATURES OF 1450* TO1550*F. DIRECTLY TO JOIN A MUCH GREATER VOLUME OF VAPORS SUPPLIED FROM ACATALYTIC CRACKING ZONE OPERATED AT TEMPERATURES OF 900 TO 1000*F. THUSRAPIDLY QUENCHING THE HIGH TEMPERATURE EFFLUENT FROM THE PARAFFINCRACKING PROCESS TO A TEMPERATURE IN THE RANGE OF 900* TO 1000*F.,SUPPLY ING THE COMBINED STREAM OF HYDROCARBON VAPORS FROM